An AFM is a device used to produce images of surface topography (and other sample characteristics) based on information obtained from rastering a sharp probe on the end of a cantilever relative to the surface of the sample. Deflections of the cantilever, or changes in its oscillation, which are detected while rastering correspond to topographical (or other) features of the sample. Deflections or changes in oscillation are typically detected by an optical lever arrangement whereby a light beam is directed onto a cantilever in the same reference frame as the optical lever. The beam reflected from the cantilever is made to illuminate a position sensitive detector (PSD). As the deflection or oscillation of the cantilever changes, the position of the reflected spot on the PSD changes, causing a change in the output from the PSD. Changes in the deflection or oscillation of the cantilever are typically made to trigger a change in the vertical position of the cantilever base relative to the sample, in order to maintain the deflection or oscillation at a constant pre-set value. It is this feedback that generates an AFM image. AFMs can be operated in a number of different imaging modes, including contact mode where the tip of the cantilever is in constant contact with the sample surface, and oscillatory modes where the tip makes no contact or only intermittent contact with the surface.
Actuators are commonly used in AFMs, for example to raster the probe relative to the sample surface or to change the position of the cantilever base relative to the sample surface. The purpose of actuators is to provide relative movement between the probe and the sample. For different purposes and different results, it may be useful to actuate the sample, or the tip or some combination of both. Sensors are also commonly used in AFMs. They are used to detect movement of various components of the AFM, including movement created by actuators. For the purposes of the specification, unless otherwise specified, the term “actuator” refers to a broad array of devices that convert input signals into physical motion, including piezo activated flexures, piezo tubes, piezo stacks, blocks, bimorphs, unimorphs, linear motors, electrostrictive actuators, electrostatic motors, capacitive motors, voice coil actuators and magnetostrictive actuators, and the term “position sensor” or “sensor” refers to a device that converts a displacement, velocity or acceleration into an electrical signal, including capacitive sensors, inductive sensors (including eddy current sensors), differential transformers (such as described in co-pending applications US20020175677A1 and US20040075428A1, Linear Variable Differential Transformers for High Precision Position Measurements, and US20040056653A1, Linear Variable Differential Transformer with Digital Electronics, which are hereby incorporated by reference in their entirety), variable inductance, optical interferometry, optical deflection detectors (including those referred to above as a PSD and those described in co-pending applications US20030209060A1 and US20040079142A1, Apparatus and Method for Isolating and Measuring Movement in Metrology Apparatus, which are hereby incorporated by reference in their entirety), strain gages, piezo sensors, magnetostrictive and electrostrictive sensors.